1. Field of Invention
The invention relates to a method for patterning a thin film on a substrate, and more particularly to a method for double patterning a thin film on a substrate.
2. Description of Related Art
In material processing methodologies, pattern etching comprises the application of a layer of radiation-sensitive material, such as photo-resist, to an upper surface of a substrate, the formation of a pattern in the layer of radiation-sensitive material using photo-lithography, and the transfer of the pattern formed in the layer of radiation-sensitive material to an underlying thin film on the substrate using an etching process. The patterning of the radiation-sensitive material generally involves exposure of the radiation-sensitive material to a pattern of electromagnetic (EM) radiation using, for example, a photo-lithography system, followed by the removal of the irradiated regions of the radiation-sensitive material (as in the case of positive tone resist), or non-irradiated regions (as in the case of negative tone resist) using a developing solution.
More recently, a double patterning approach has been introduced to allow the patterning of smaller features at a smaller pitch than what is currently possible with standard lithographic techniques. One approach to reduce the feature size is to use standard lithographic pattern and etch techniques on the same substrate twice (i.e., LELE, or Litho/Etch/Litho/Etch), thereby forming larger patterns spaced closely together to achieve a smaller feature size than would be possible by single exposure. During LELE double patterning, the substrate is exposed to a first pattern, the first pattern is developed in the radiation-sensitive material, the first pattern formed in the radiation-sensitive material is transferred to an underlying layer using an etching process, and then this series of steps is repeated for a second pattern.
Another approach to reduce the feature size is to use standard lithographic pattern on the same substrate twice followed by etch techniques (i.e., LLE, or Litho/Litho/Etch), thereby forming larger patterns spaced closely together to achieve a smaller feature size than would be possible by single exposure. During LLE double patterning, the substrate is exposed to a first pattern, the substrate is exposed to a second pattern, the first pattern and the second pattern are developed in the radiation-sensitive material, and the first pattern and the second pattern formed in the radiation-sensitive material are transferred to an underlying layer using an etching process.
One approach to LLE double patterning includes a Litho/Freeze/Litho/Etch (LFLE) technique that utilizes an application of a freeze material on a first pattern in a first patterning layer to cause “freezing” or cross-linking therein, thus allowing the first patterning layer to withstand subsequent processing of a second patterning layer with a second pattern. However, conventional LFLE double patterning techniques still have a limit to the ultimate feature size that is printable.